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MOX Progress, plus Inconsistency from UCS

Nuclear disarmament took a big step forward on Monday, when the U.S. and Russia announced a new agreement on disposition of surplus plutonium. Each country had previously agreed to dispose of 34 metric tons of surplus weapons-grade plutonium by using it in mixed-oxide (plutonium-uranium) fuel, also known as MOX, but there were disagreements on how to do it. Monday's agreement notes that the U.S. will use the plutonium in light-water reactors, whereas Russia will use it in fast-spectrum reactors. The distinction may seem slight, but it had been a significant point of contention. The agreement clears the way for removing a significant amount of weapons-grade material.

You might think that such news would meet with hearty and uniform approbation, but it did not, particularly at the Union of Concerned Scientists. This time, their "concern" is about the BN-600 and BN-800 reactors that the Russians plan to use. As reported by Newsday,

Ed Lyman, nuclear weapons expert at the Union of Concerned Scientists, saiduse of the relatively small BN600 reactor "will put Russian plutoniumdisposition on the slow track" because the reactor can burn only aboutthree-tenths of a ton of plutonium a year, and the larger [BN-800] reactor hasyet to be built.

Lyman said "this is a total retreat from the original concept" whichwould have disposed of the plutonium in larger light-water reactors, an optionthe Russian[s] rejected.

It should be noted that "has yet to be built" is misleading. Construction of the BN-800 began in 2002, and its scheduled completion date precedes the scheduled date for the U.S. to begin production of commercial MOX fuel batches.

More notable is that the complaint comes from Ed Lyman. In 2004, he sang a very different song to an Atomic Safety and Licensing Board as he used the flimsiest of evidence in an attempt to block the use of MOX in U.S. light-water reactors. Does he want to see plutonium destroyed, or doesn't he?

It makes you wonder whether the "C" in "UCS" really stands for "contrary".

Alex, you can do either with FBR, depending on the core configuration you chose. With the breeding blanket you get more Pu and your FBR is a "breeder", without the breeding blanket (just the reflector), then you get a "burner".

False dilemma, which ignores the vitrification option for direct disposal of surplus separated Pu as waste. It was part of DOE's original two-track approach approved in 1996, but the Bush administration killed off the vitrification portion, probably because it doesn't involve using a reactor.

Alex, breeding is sometimes done by having a critical core surrounded by a breeding blanket; that blanket is a collection of rods of metal-clad uranium dioxide, like fuel rods, but the uranium in them is depleted, so the neutrons coming from the core do not induce much fission in them, but do convert many 238-U nuclei to 239-Pu.

Remove the breeding blanket and the outward-flying neutrons are wasted; the breeding ratio drops below 1.0.

Alex: I'm not a nuclear physicist, but the basic explanation is that an atom of uranium-238 gets turned into plutonium when a neutron bumps into it and "sticks".

In a nuclear reactor, neutrons are released when the fissile material - uranium-235 or plutonium-239 - undergoes fission. So, in every nuclear reactor where the fuel contains u-238, you will breed at least some plutonium.

Most conventional power reactors out there don't result in enough plutonium being produced to outweigh the u-235 lost, though they do get considerably more energy from their fuel than they otherwise would if "breeding" didn't occur. However, a breeder reactor is specially designed to ensure that the ratio of plutonium atoms created to atoms fissioned is greater than one. That is, on average, more than one neutron from every fissioning atom goes on to make a new plutonium atom.

One analogy you could use is that U-238 represents wet wood, and breeding is like putting the wood near a fire to dry. You can end up with more dry wood than you started with.

Well, I believe that work on the BN-800 was really started back in the 1980s. I don't know whether this went much beyond site preparation, but my old Soviet books discuss the design of the plant. The decision to complete the reactor was apparently made fairly soon after Putin entered office, and I imagine that work has been ongoing (in the Russian sense) ever since then- meaning concrete advances only started materializing last year. So in a way, 2002 and 2006 are both right.

Also, the BN-600 has never bred Pu in its 27 years of operation. It's always been fueled with highly-enriched uranium.

Alex, from my limited understanding, breeder reactors can operate at breeding levels below one, ie slowly reducing active material, if required. However one point of importance is that plutonium for bombs has to be a relatively pure isotope (Pu-239), which is certainly not true of fuel that has been inside a reactor for a couple of years; so in terms of bomb function, the plutonium is rendered useless.

Plutonium and uranium are loaded into a breeder reactor. The plutonium fissions and produces the power. A portion of the uranium is converted to plutonium (Pu-239) by operation of the reactor. Pu-239 is a fissile fuel that can be put into another reactor. A breeder reactor is so efficient at converting uranium to plutonium that more fissile Pu is created than is destroyed by running the reactor. Hope that makes sense.

Thanx very much for the answers,very interesting. I have some other considerations to do:1) If we operate a fast reactor as a "burner" (not as a breeder), what about the rate of elimination of plution isotopes (and all transuranics, at this point, I suppose) for example per TWh or GWyear of the fast reactor electricity production? I mean, how many GW of fast reactor we shoul build and operate to burn the transuranics inventory generated from a fleet of, say, ten or twenty 1 GW LWR?2) What about % of fissile isotopes of plutonium in a fast *breeder* reactor (seed and blanket) vs a LWR one?3) For "Sovietologist", I don't understand your statement : even BN-600 use high enriched uranium (which %?... I'm curious), it actually converts in plutonium some uranium 238,maybe with a breeding ratio a lot lower than one, am I wrong?

"However one point of importance is that plutonium for bombs has to be a relatively pure isotope (Pu-239), which is certainly not true of fuel that has been inside a reactor for a couple of years; so in terms of bomb function, the plutonium is rendered useless."

That's absolutely untrue, according to US DOE and the National Academy of Sciences, among other qualified sources. Weapons grade Pu is preferred for weapons applications, but reactor grade Pu can be and has been used in nuclear explosives. Demonstrated by US underground testing in the 1960s, results declassified in the 1970s.

Thanx very much for the answers,very interesting I have some other considerations to do:1) If we operate a fast reactor as a "burner", what about the rate of elimination of plution isotopes (and all transuranics, at this point, I suppose) for example per TWh or GWyear of the fast reactor electricity production? I mean, how many GW of fast reactor we shoul build and operate to burn the transuranics inventory generated from a fleet of, say, ten 1 GW LWR?2) What about % of fissile isotopes of plutonium in a fast *breeder* reactor (seed and blanket) vs a LWR one?3) For sovietologist, I don't understand your statement : even BN-600 uses high enriched uranium (which %?... I'm curious), it actually converts in plutonium some uranium 238,maybe with a breeding ratio a lot lower than one, am I wrong?

I realize now that I mistyped: I meant to say that the BN-600 has never been fueled with Pu. I was actually wrong about this- a small number of MOX fuel assemblies were tested in the reactor, but in regular practice it's been fueled with 17-25% enriched UO2. At the same time, I don't believe that it has demonstrated actual breeding either (i.e., producing more usable fuel than it consumes.) It produces some plutonium, but so do all reactors containing U-238. I'm not sure how efficiently the reactor produces Pu-239- it's probably dependent on a large number of factors- fuel enrichment, burnup, etc.

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